Implementing blind tuning in hybrid MIMO RF beamforming systems

ABSTRACT

A system and a method for applying a blind tuning process to M antennas coupled via N beamformers to a multiple input multiple output (MIMO) receiving system having N channels, wherein M&gt;N, are provided herein. The method includes the following steps: Periodically measuring channel fading rate at a baseband level to determine the number of antennas L out of K antennas connected to each one of the beamformers, to be combined at each one of the N beamformers; assigning the antennas to the subset L according to some criteria such as best quality indicator; repeatedly applying a tuning process to L antennas in each one of the N beamformers.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S.non-provisional patent application Ser. No. 13/770,255 filed on Feb. 19,2013, which is a continuation-in-part application of U.S.non-provisional patent application Ser. No. 13/630,146 filed on Sep. 28,2012, which in turn claims benefit from U.S. provisional patentapplications 61/652,743 filed on May 29, 2012; 61/657,999 filed on Jun.11, 2012; and 61/665,592 filed on Jun. 28, 2012; U.S. non-provisionalpatent application Ser. No. 13/770,255 further claims benefit from U.S.provisional patent applications: 61/658,015 filed on Jun. 11, 2012; and61/671,408 filed on Jul. 13, 2012, all of which are incorporated hereinin their entirety.

FIELD OF THE INVENTION

The present invention relates generally to the field of radio frequency(RF) multiple-input-multiple-output (MIMO) systems and in particular tosystems and methods for improving performance of MIMO systems by RFbeamforming.

BACKGROUND OF THE INVENTION

Prior to setting forth a short discussion of the related art, it may behelpful to set forth definitions of certain terms that will be usedhereinafter.

The term “MIMO” as used herein, is defined as the use of multipleantennas at both the transmitter and receiver to improve communicationperformance. MIMO offers significant increases in data throughput andlink range without additional bandwidth or increased transmit power. Itachieves this goal by spreading the transmit power over the antennas toachieve spatial multiplexing that improves the spectral efficiency (morebits per second per Hz of bandwidth) or to achieve a diversity gain thatimproves the link reliability (reduced fading), or increased antennadirectivity.

The term “beamforming” sometimes referred to as “spatial filtering” asused herein, is a signal processing technique used in antenna arrays fordirectional signal transmission or reception. This is achieved bycombining elements in the array in such a way that signals at particularangles experience constructive interference while others experiencedestructive interference. Beamforming can be used at both thetransmitting and receiving ends in order to achieve spatial selectivity.

The term “beamformer” as used herein refers to RF circuitry thatimplements beamforming and usually includes a combiner and may furtherinclude switches, controllable phase shifters, and in some casesamplifiers and/or attenuators.

The term “Receiving Radio Distribution Network” or “Rx RDN” or simply“RDN” as used herein is defined as a group of beamformers as set forthabove.

The term “hybrid MIMO RDN” as used herein is defined as a MIMO systemthat employs two or more antennas per channel (N is the number ofchannels and M is the total number of antennas and M>N). Thisarchitecture employs a beamformer for each channel so that two or moreantennas are combined for each radio circuit that is connected to eachone of the channels.

In hybrid MIMO RDN receiving systems, when the phases of the receivedsignals from each antenna are properly adjusted or tuned with respect toone another, the individual signals may be combined and may result in animproved SNR or data throughput for the receiving system.

One tuning phase method is based on channel estimation of each antennawhich contributes to the beamforming; the invention here is using adifferent method for identifying best-phase alignments for beamformingpurposes; it is based on modifying phases iteratively while monitoringtheir combined signal quality.

When more than two antennas are involved, the number of iterationincreases, thus longer periods of quasi-static fading are needed forstable process, as well as mechanism to address cases where quasi-staticfading ceases to exist.

For example, in Cellular protocols, quality indicators are typicallyrepeated ˜1000-2000 times per second. In WiFi protocols, they may havelower repetition rates, depending on traffic and number of users. InMobile environment, fading change rate may vary between ˜10 times asecond (static environment) and 100-200 times a second (vehicular),although it can be as fast as 1000-2000 times per second.

Consequently, when multiple antennas beamforming is based on aniterative process, it has to strike a balance between using the maximumnumber of available antennas, and the need to update each one of themfast enough to trace the fading variations.

As discussed above, various methods are known in the art for tuning ofmultiple-antenna beamformers. Each method has its advantages anddisadvantages. One method is based on making a direct measurement of theantennas' signals phases & amplitudes and calculates correspondingcorrections (can be carried out via channel estimation). Another methodincludes trying out various possible solutions and grading them pertheir impact on various quality indicators. This can be carried out viablind search of the best set of phases where there is a systematicgradient seeking method, or via blind scan where there is preference totry each and every possible phase value, or some other method wheretrial and error are the driver of the tuning process. All of these trialand error methods, including blind scan and blind search, are referredherein as “blind beamforming tuning algorithms” or simply: “blindalgorithms”.

It is generally agreed that while channel estimation based method is thefaster tuning method, it is not always the preferred one. For instance,in some cases, channel estimation requires digging info that may not beprovided over standard signals coming out of baseband processors, whilequality indicators needed for blind search may be readily available.Another consideration relates to dealing with interference—whereco-channel undesired signals dominate, and when the receiver does notallocate resources for interference cancellation, then blind scan mayyield better results (e.g., maximize the overall data rates).

SUMMARY

The present invention, in embodiments thereof, addresses the challengederiving from the fact that blind algorithms with multiple antennasrequire relatively long convergence time. Embodiments of the presentinvention continuously update the beamforming process based on thefading environment. More specifically, by applying trade-offs among theparticipating antennas, algorithm resolution, and algorithm stability,embodiments of the present invention provide means for exploiting theavailable tools that can still be used without causing the algorithm tolose track. Therefore, a robust convergence metric is employed.

According to some embodiments of the present invention, a system forselecting a subset of L antennas from K antennas in each beamformer outof N beamformers is provided herein. The system includes amultiple-input-multiple-output (MIMO) receiving system comprising a MIMObaseband module having N branches; a radio distribution network (RDN)connected to the MIMO receiving system, the RDN comprising at least onebeamformer, wherein each one of the beamformers is fed by two or moreantennas, so that a total number of antennas in the system is M, whereinM is greater than N, wherein each one of the beamformers includes atleast one combiner configured to combine signals coming from theantennas coupled to a respective beamformer into a combined signal,wherein the baseband module comprises an antenna subset selection moduleconfigured to: derive Mobility Monitoring Indicators (MMI) associatedwith the MIMO receiving system, and use a look up table to map MMI foreach of the L antennas in each beamformer. Then the L antennas are eachtuned over time using blind search/scan.

These additional, and/or other aspects and/or advantages of the presentinvention are set forth in the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and in order to show how itmay be implemented, references are made, purely by way of example, tothe accompanying drawings in which like numerals designate correspondingelements or sections. In the accompanying drawings:

FIG. 1 is a high level block diagram illustrating a system according tosome embodiments of the present invention;

FIG. 2 is a block diagram illustrating a an aspect according toembodiments of the present invention;

FIG. 3 is a flowchart diagram illustrating the blind search process withantenna subset selection according to embodiments of the presentinvention;

FIG. 4 is a flowchart diagram illustrating a subroutine to calculateTotal Data Throughput Indicator (TDTI) according to some embodiments ofthe present invention;

FIG. 5 is a flowchart diagram illustrating a subroutine for antennasgrading according to embodiments of the present invention;

FIG. 6 is a flowchart diagram illustrating a subroutine for coarse blindtuning according to embodiments of the present invention;

FIG. 7 is a flowchart diagram illustrating a subroutine for fine blindtuning according to embodiments of the present invention;

FIGS. 8 and 9 are circuit diagrams illustrating exemplaryimplementations of the system according to embodiments of the presentinvention; and

FIG. 10 is a high level flowchart illustrating a method according tosome embodiment of the present invention.

The drawings together with the following detailed description make theembodiments of the invention apparent to those skilled in the art.

DETAILED DESCRIPTION

With specific reference now to the drawings in detail, it is stressedthat the particulars shown are for the purpose of example and solely fordiscussing the preferred embodiments of the present invention, and arepresented in the cause of providing what is believed to be the mostuseful and readily understood description of the principles andconceptual aspects of the invention. In this regard, no attempt is madeto show structural details of the invention in more detail than isnecessary for a fundamental understanding of the invention. Thedescription taken with the drawings makes apparent to those skilled inthe art how the several forms of the invention may be embodied inpractice.

Before explaining the embodiments of the invention in detail, it is tobe understood that the invention is not limited in its application tothe details of construction and the arrangement of the components setforth in the following descriptions or illustrated in the drawings. Theinvention is applicable to other embodiments and may be practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

FIG. 1 is a high level block diagram illustrating a system according toembodiments of the present invention. System 100 is a MIMO receivingsystem in a hybrid MIMO RDN configuration. In the hybrid MIMO RDNconfiguration, baseband module 120 receives N branches and is configuredto operate, on the baseband level, in accordance with any known orlegacy MIMO receiving scheme. System 100 further includes a radiodistribution network 110 (RDN) connected to baseband module 120 viaradio circuits 12-1 to 12-N. RDN 110 includes at least one beamformerwith antenna amplification or attenuation functionality such as 140-1and 140-N, being fed by two or more antennas such as 10-1-1 to 10-1-K₁through 10-N-1 to 10-N-K_(N), so that a total number of antennas insystem 100 is M=K₁+K₂+ . . . +K_(N), wherein M is greater than N.Additionally, each one of the beamformers includes a combiner (not shownhere) configured to combine signals coming from the antennas into asingle combined signal converted to baseband by radio module 12-1 to12-N. Baseband module 120 is configured, among other things, to tune RDN110, for example by adjusting phase shifters located within beamformers140-1 to 140-N. System 100 further includes antenna subset selection andtuning module 130.

In operation, antenna subset selection and tuning module 130 iterativelyselects specific subset L of the K antennas on each one of the Nbeamformers, based on quality indicators being a subset of the bestperforming antennas from each group of antennas such as 10-1-1 to10-1-K₁ through 10-N-1 to 10-N-K_(N). The quality indicator may be, forexample, a respective contribution to the total data rate of theantennas. It then applies a blind algorithm while constantly monitoringthe fading rate change and adjusting the number of antennasparticipating in the blind algorithm accordingly.

FIG. 2 is a block diagram illustrating an aspect according to someembodiments of the present invention. The diagram provides a partialview of a hybrid MIMO RDN receiving system 200 that includes Nbeamformers 240-1 to 240-N. As can be seen, each beamformer is fed by Kantennas. During the aforementioned selection process, a subset of Lantennas is selected for participating in the blind algorithm processwhich involves iterative tuning of the antennas as will be explainedbelow.

FIG. 3 is a flowchart diagram illustrating the blind search process withantenna subset selection according to embodiments of the presentinvention. Process 300 begins with step 310 where it measures MobilityMonitoring Indicators (MMI). Step 320 sets a revisit time T, being thetime after which the channel may no longer be regarded as having thesame characteristics so that the blind tuning process needs to berestarted from step 310. Then, process 300 goes to step 330 of gradingeach antenna by their Total Data Throughput Indicator (TDTI) usingsubroutine 300 so that grading each one of the K antennas, is based ontheir total data throughput coming from various data streams and whereinthe selecting of said specific subset L is based on the total datathroughput grades of the K antennas. The method then goes to step 340for selecting the number of L antennas to participate in the beamformingthat is predicted to require tuning process period short enough to fitinto a quasi-static assumption associated with a given MMI value. L is asubset of antennas from K which is the number of the antennas on eachbeamformer. The TDTI is measured for each one of the K antennas and theL antennas with the highest TDTI are selected for the beamformer. AfterL antennas are selected, a beamforming coarse tuning algorithm iscarried out in step 350. Next, step 360 executes fine tuning of thebeamformer by subroutine 600 of FIG. 6 and goes to step 370. Step 370goes to step 360 for continuing fine tuning if Timer T is not expired.Otherwise, step 370 will go to step 310 for measuring MMI again.

In some embodiments, the sub process in step 310 may start off with acontinuous monitoring of MMI which may be performed by the receiver,e.g. by measuring Doppler, or measuring Pilot strength change rate, orother receiver quality indicators, providing a lookup table that is usedto map estimated fading rate change or MMI into preferred number L outof K antennas used for beamforming.

Thus, the quality indicators are derivable from the lookup table. Thelookup table will use a Mobility Monitor Indicator MMI, which will haveseveral ranges as follows:

For 0 > MMI > THRSH 1 boundaries of Static For THRESH 1 > MMI > THRSH 2boundaries of Pedestrian For THRESH k > MMI > THRSH k + 1 boundariesvehicular k

The criterion for selecting a given antenna out of the K possible intothe subset L for a given beamformer is TDTI for each antenna. Therefore,from time to time all antennas, the ones currently used in the subset,as well as the ones that are not, will be graded. Consequently, antennasselected for the subset will be the best L antennas, in terms of TDTI,out of K in each one of the N beamformers.

FIG. 4 is a flowchart diagram illustrating a subroutine 400 to calculateTDTI according to some embodiments of the present invention. Process 410retrieves SINR for each layer from the baseband processor. Then, process420 converts SINR to throughput indicator using CQI_TBS lookup table.One example of an embodiment for estimating total data throughput bySINRs and a CQI_TBS lookup table is described next. For the downlinkdata transmissions, the NodeB typically selects the modulation schemeand code rate depending on the Channel Quality Indicator (CQI) feedbacktransmitted by the User Equipment (UE) in the uplink. The reported CQIis not a direct indication of SINR. Instead, the UE reports the highestMCS (Modulation and Coding Scheme) that it can decode with a transportblock error rate probability not exceeding 10% taking into account boththe characteristics of the UE's receiver and radio channel quality. InLTE SU-MIMO spatial multiplexing scheme, at most two codewords are used,even if four layers are transmitted. Only one CQI and HARQ ACK/NACKfeedback reporting is needed for all layers in one codeword, since allRBs belonging to the same codeword use the same MCS, even if a codewordis mapped to multiple layers. Process 430 calculates the TDTI based onSINRs and the CQI_TBS table by the following formula.

${{TDTI} = {\sum\limits_{i = 1}^{N_{d}}{{TBS}( {SINR}_{i} )}}},$for N_(d) data streams, where TBS(SINR_(i)) can be calculated by thefloor function or by interpolation between two SINR entries in thetable. Then, process 440 updates SINRs entries corresponding CQI in thelookup table when UE reports CQI feedback to NodeB. According to someembodiments, the SINR conversion in the lookup table is updated in acase a new CQI report arrives.

TABLE 1 CQI_TBS Lookup Table CQI 1st Codeword 2nd Codeword IndexModulation MCS TBS SINR (dB) SINR (dB) 0 1 QPSK 0 536 2.0 1.5 2 QPSK 0536 3.9 3.4 3 QPSK 2 872 5.9 5.4 4 QPSK 5 1736 7.8 7.3 5 QPSK 7 2417 9.79.2 6 QPSK 9 3112 11.6 11.1 7 16QAM 12 4008 13.6 13.1 8 16QAM 14 516015.5 15.0 9 16QAM 16 6200 17.4 16.9 10 64QAM 20 7992 19.4 18.9 11 64QAM23 9912 21.3 20.8 12 64QAM 25 11448 23.2 22.7 13 64QAM 27 12576 25.124.6 14 64QAM 28 14688 27.1 26.6 15 64QAM 28 14688 29.0 28.5

FIG. 5 is a flowchart diagram illustrating a subroutine for antennagrading according to embodiments of the present invention. Subroutine500 starts with selecting a specific beamformer for antenna grading atstep 510. Then, step 520 keeps the other beamformers connected with thesame settings using K or less antennas throughout the antenna gradingsubroutine for the selected beamformer. Intuitively, the otherbeamformers can provide beamforming gain, reduce overall noise ofreceived signals and improve grading accuracy of the selectedbeamformer. Step 530 isolates the next antenna in the selectedbeamformer for grading. Next, step 540 measures SINR per layer with theselected beamformer using the isolated antenna and the other beamformersusing K or less antennas as configured by step 520. All beamformers areconnected to their respective radios. Step 550 calculates TDTI from themeasured SINRs using CQI_TBL lookup table, and the TDTI is then assignedas the grade of the isolated antenna. Finally, step 560 exits if allantennas of the selected beamformer have been graded. Otherwise, it goesback to step 530 for grading the next antenna.

The effect of beamforming on reducing noise of received signals can beillustrated by the following example. Let X be a matrix denoting signalsbeing transmitted and H denote the channel matrix modeling thepropagation. Then the signals received by the receiver can be written asY=HWX+N,where N is the additive noise matrix and W is the weights matrix.

For 2×2 channels, the matrices can be noted as

${Y = \begin{bmatrix}y_{1} \\y_{2}\end{bmatrix}},{H\begin{bmatrix}h_{11} & h_{12} \\h_{21} & h_{22}\end{bmatrix}},{W = \begin{bmatrix}k_{1} & 0 \\0 & k_{2}\end{bmatrix}},{X = \begin{bmatrix}x_{1} \\x_{2}\end{bmatrix}},{N = \begin{bmatrix}n_{1} \\n_{2}\end{bmatrix}},$then Y=HWX+N can be written as

$\begin{bmatrix}y_{1} \\y_{2}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} \\h_{21} & h_{22}\end{bmatrix}\begin{bmatrix}k_{1} & 0 \\0 & k_{2}\end{bmatrix}}\begin{bmatrix}x_{1} \\x_{2}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2}\end{bmatrix}}$Assuming that the receiver has the knowledge of H and W, the transmittedsignals can be recovered as:

     X̂ = (H W)⁻¹Y = (H W)⁻¹(H WX + N) = X + (WH)⁻¹N, where${H^{- 1} = {{\frac{1}{{h_{11}h_{22}} - {h_{12}h_{21}}}\begin{bmatrix}h_{22} & {- h_{12}} \\{- h_{21}} & h_{11}\end{bmatrix}} = \begin{bmatrix}a & b \\c & d\end{bmatrix}}},{W^{- 1}\begin{bmatrix}\frac{1}{k_{1}} & 0 \\0 & \frac{1}{k_{2}}\end{bmatrix}}$The error of recovered signals can be derived as

$E = {\begin{bmatrix}e_{1} \\e_{2}\end{bmatrix} = {{\hat{X} - X} = {{W^{- 1}H^{- 1}N} = \begin{bmatrix}\frac{{an}_{1} + {bn}_{2}}{k_{1}} \\\frac{{cn}_{1} + {dn}_{2}}{k_{2}}\end{bmatrix}}}}$If channels from transmitter 1 and transmitter 2 are improved by afactor of k₁ and k₂ respectively (i.e., k₁>1 and k₂>1), then the errorfor x₁ and x₂ are reduced by a factor of 1/k₁ and 1/k₂.

FIG. 6 is a flowchart diagram illustrating a subroutine for a round ofcoarse blind tuning for a beamformer according to an exemplaryembodiment of the present invention. Subroutine 600 begins with step 610where it picks the best antenna among L selected antennas to participatein the beamformer according to its grade determined by the antennagrading subroutine 500. Step 620 adds the next best antenna intobeamformer and measures TDTI using TDTI calculation routine as describedin FIG. 4. Then, step 630 changes (or ‘flips’) the added antenna's phaseby 180° and measures TDTI again. Next, step 640 chooses the better phasefor the added antenna. Finally, step 650 goes to step 620 for addingnext antenna until all L selected antennas have been included for thebeamformer. During coarse blind tuning of the beamformer, more phasesmay be tested instead of just two phases, 0° and 180° as depicted insteps 630 and 640. For example, 0°, 120° and 240° may be used.

FIG. 7 is a flowchart diagram illustrating a subroutine for fine blindtuning according to an exemplary embodiment of the present invention.All selected antennas stay connected to the beamformer during the finetuning process. Subroutine 700 begins with step 710 where it picks thebest antenna among L selected antennas in the beamformer according toits grade determined by the antenna grading subroutine 500. Step 720modifies the next best antenna's initial phase by about 90° on onedirection (e.g., clockwise) and compares TDTI of modified to initialphase. Then, step 730 keeps the new phase and goes to step 770 if TDTIimproves. Otherwise, it goes to next step 740. Step 740 modifies thenext best antenna's phase by 180° to the other direction (e.g. counterclockwise) and compares TDTI of modified to initial phase. Then, step750 keeps the new phase and goes to step 770 if TDTI improves.Otherwise, it goes to next step 760 to keep the original phase. Finally,step 770 goes to step 720 for fine tuning the next antenna until all Lselected antennas have been fine tuned. During fine blind tuning of aselected antenna, other finer than 90° phase resolution may be tested.For example, 45° or 60° may be used.

FIG. 8 and FIG. 9 are circuit diagrams illustrating exemplaryimplementations of the system according to embodiments of the presentinvention. Specifically, exemplary implementations of the beamformersoperate in cooperation with antenna subset selection module 130. Asopposed to the preferred implementation for RDN that use ChannelEstimation for tuning, the Blind algorithm RDN implementation will havephase tuning for all antennas, including the MAIN. As opposed to theimplementation for RDN that use Channel Estimation for tuning, the BlindRDN tuning implementation will have a set of N-1 combiners, allowing forcombining only 2 antennas or only 3 antennas etc., to be selected perthe measured fading rate change or MMI. As opposed to the preferredimplementation for RDN that use Channel Estimation for tuning, the BlindTuning RDN implementation will have pooling scheme allowing selecting anumber of antennas for combining

FIG. 8 depicts an example of five antennas 801 to 805, each connected toa diversity module 810A to 810E where the diversity module controlsphase and amplitude. The diversity modules are feeding 1:8 selectors830A to 830E that are feeding a 1:5 RF combiner 840. The 1:8 selectorsare also feeding three-way combiners 820A to 820J so that varioustriplets of antennas can be combined. A sixteen-way selector 850 selectsalternative combiners including the single 1:5 combiner and the ten 1:3combiners. Consequently, any three antennas out of five can be combinedand selected as the input of a radio, as well as all five antennascombined. As shown in FIG. 8, the circuit is capable of isolating eachantenna by routing the “bypass” signals from the antennas. In generaland in this example, the grading of each one of the K antennas may becarried out by a process that includes isolating a given antenna andregistering the reported signal to noise plus interference ratio (SINR)of each layer; converting each SINR to CQI and then to Data Rate viasaid lookup table; and summing them up to provide TDTI grading, whilesaid process is carried out with K or less antennas at the otherbeamformers.

FIG. 9 depicts an example of four antennas 901 to 904, each connected toa diversity module 910A to 910D. The diversity modules are feeding 1:5selectors 920A to 920D that are feeding a 1:4 RF combiner 940. The 1:5selectors are also feeding three-way combiners 930A to 930D so thatvarious triplets of antennas can be combined. A nine-way selector 950selects alternative combiners including the single 1:4 combiner and thefour 1:3 combiners. Consequently, any three antennas out of four can beselected as inputs of a radio, as well as all four antennas combined.

FIG. 10 is a high level flowchart illustrating a method 1000 accordingto some embodiment of the present invention. It should be understoodthat method 1000 is not limited to an implementation using theaforementioned exemplary architecture discussed above. Method 1000 mayinclude the following stages: receiving multiple input multiple output(MIMO) radio frequency (RF) signals through M antennas coupled via Nbeamformers to a MIMO receiving system having N channels, wherein M>N1010; measuring channel fading rate at a baseband level 1020;determining a number of antennas L to be combined out of K antennas ofeach one of the N beamformers, based on the measured fading rate 1030;and repeatedly or iteratively applying a tuning process to L antennas ateach of the N beamformers 1040, wherein the repeated tuning ends whenall L antennas are tuned but preferably before the channel fading ratehas been changed.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or an apparatus.Accordingly, aspects of the present invention may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.”

The aforementioned flowchart and block diagrams illustrate thearchitecture, functionality, and operation of possible implementationsof systems and methods according to various embodiments of the presentinvention. In this regard, each block in the flowchart or block diagramsmay represent a module, segment, or portion of code, which comprises oneor more executable instructions for implementing the specified logicalfunction(s). It should also be noted that, in some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts, or combinations of special purpose hardware andcomputer instructions.

In the above description, an embodiment is an example or implementationof the inventions. The various appearances of “one embodiment,” “anembodiment” or “some embodiments” do not necessarily all refer to thesame embodiments.

Although various features of the invention may be described in thecontext of a single embodiment, the features may also be providedseparately or in any suitable combination. Conversely, although theinvention may be described herein in the context of separate embodimentsfor clarity, the invention may also be implemented in a singleembodiment.

Reference in the specification to “some embodiments”, “an embodiment”,“one embodiment” or “other embodiments” means that a particular feature,structure, or characteristic described in connection with theembodiments is included in at least some embodiments, but notnecessarily all embodiments, of the inventions.

It is to be understood that the phraseology and terminology employedherein is not to be construed as limiting and are for descriptivepurpose only.

The principles and uses of the teachings of the present invention may bebetter understood with reference to the accompanying description,figures and examples.

It is to be understood that the details set forth herein do not construea limitation to an application of the invention.

Furthermore, it is to be understood that the invention can be carriedout or practiced in various ways and that the invention can beimplemented in embodiments other than the ones outlined in thedescription above.

It is to be understood that the terms “including”, “comprising”,“consisting” and grammatical variants thereof do not preclude theaddition of one or more components, features, steps, or integers orgroups thereof and that the terms are to be construed as specifyingcomponents, features, steps or integers.

If the specification or claims refer to “an additional” element, thatdoes not preclude there being more than one of the additional element.

It is to be understood that where the claims or specification refer to“a” or “an” element, such reference is not be construed that there isonly one of that element.

It is to be understood that where the specification states that acomponent, feature, structure, or characteristic “may”, “might”, “can”or “could” be included, that particular component, feature, structure,or characteristic is not required to be included.

Where applicable, although state diagrams, flow diagrams or both may beused to describe embodiments, the invention is not limited to thosediagrams or to the corresponding descriptions. For example, flow neednot move through each illustrated box or state, or in exactly the sameorder as illustrated and described.

Methods of the present invention may be implemented by performing orcompleting manually, automatically, or a combination thereof, selectedsteps or tasks.

The term “method” may refer to manners, means, techniques and proceduresfor accomplishing a given task including, but not limited to, thosemanners, means, techniques and procedures either known to, or readilydeveloped from known manners, means, techniques and procedures bypractitioners of the art to which the invention belongs.

The descriptions, examples, methods and materials presented in theclaims and the specification are not to be construed as limiting butrather as illustrative only.

Meanings of technical and scientific terms used herein are to becommonly understood as by one of ordinary skill in the art to which theinvention belongs, unless otherwise defined.

The present invention may be implemented in the testing or practice withmethods and materials equivalent or similar to those described herein.

While the invention has been described with respect to a limited numberof embodiments, these should not be construed as limitations on thescope of the invention, but rather as exemplifications of some of thepreferred embodiments. Other possible variations, modifications, andapplications are also within the scope of the invention. Accordingly,the scope of the invention should not be limited by what has thus farbeen described, but by the appended claims and their legal equivalents.

We claim:
 1. A method comprising: receiving multiple input multipleoutput (MIMO) radio frequency (RF) signals through M antennas coupledvia N beamformers to a MIMO receiving system having N channels, whereinM>N; measuring channel fading rate at a baseband level; grading each oneof K antennas, based on their total data throughput coming from variousdata streams, wherein the total data throughput is represented by atotal data throughput indicator (TDTI); determining a number of antennasL to be combined out of the K antennas of each one of the N beamformers,based on the measured fading rate, wherein the selecting of saidspecific subset L is based on the total data throughput grades of the Kantennas; and repeatedly applying a tuning process to L antennas at eachof the N beamformers, wherein the tuning process comprises adjusting aphase of each of said L antennas to maximize a TDTI.
 2. The methodaccording to claim 1, further comprising selecting a specific subset Lof the K antennas on each one of the N beamformers, based on qualityindicators.
 3. The method according to claim 2, wherein the qualityindicator is respective contribution to total data rate.
 4. The methodaccording to claim 1, wherein the channel fading rate is represented bymeasuring a mobility monitoring indicator (MMI).
 5. The method accordingto claim 1, wherein the TDTI is derivable via a lookup table based on achannel quality indicator (CQI) criterion and measured signal to noiseplus interference ratio (SINR).
 6. The method according to claim 1,wherein the grading of each one of the K antennas is carried out by aprocess comprising: isolating a given antenna and registering thereported signal to noise plus interference ratio (SINR) of each layer;converting each SINR to channel quality indicator (CQI) and then to DataRate via said lookup table; and summing the Data Rates to provide totaldata throughput indicator (TDTI) grading, while said process is carriedout with K or less antennas at the other beamformers.
 7. The methodaccording to claim 6, further comprising a step of updating the SINRconversion in the lookup table in a case a new CQI report arrives. 8.The method according to claim 1, wherein said tuning process includes atleast one round of coarse tuning process.
 9. The method according toclaim 1, wherein said tuning process includes a fine tuning process. 10.A method comprising: receiving multiple input multiple output (MIMO)radio frequency (RF) signals through M antennas coupled via Nbeamformers to a MIMO receiving system having N channels, wherein M>N;measuring channel fading rate at a baseband level; determining a numberof antennas L to be combined out of K antennas of each one of the Nbeamformers, based on the measured fading rate; and repeatedly applyinga tuning process to L antennas at each of the N beamformers, whereinsaid tuning process includes at least one round of coarse tuningprocess, said coarse tuning process comprising: selecting best gradedantenna as an anchor; combining the anchor with the second best gradedantenna and measure Total Data Throughput Indicator (TDTI); flipping thephase of the second best antenna by approximately 180°, and measuringthe TDTI; choosing the better TDTI as preferred coarse phase; combiningthe next best graded antenna with the previously combined antennas andmeasure the TDTI; flipping the phase of the next best graded antenna andmeasure TDTI, and selecting the better TDTI as preferred coarse phasefor the next best graded antenna; repeating the adding of antennas tothe combiner per their grading until all L antennas are added.
 11. Asystem comprising M antennas; N beamformers connected to the M antennas;a multiple input multiple output (MIMO) receiving system having Nchannels, connected to the N beamformers, wherein M>N; and an antennasubset selection and tuning module configured to: measure channel fadingrate at a baseband level; grade each one of the K antennas, based ontheir total data throughput coming from various data streams, whereinthe total data throughput is represented by a total data throughputindicator (TDTI); determine a number of antennas L≦K to be combined ateach one of the N beamformers, wherein K is a number of antennasconnected to each one of the beamformers, based on the measured fadingrate, wherein the selecting of said specific subset L is based on thetotal data throughput grades of the K antennas; and repeatedly apply atuning process to L antennas at each of the N beamformers, wherein thetuning process comprises adjusting a phase of each of said L antennas tomaximize a TDTI.
 12. The system according to claim 11, wherein theantenna subset selection and tuning module is further configured toselect a specific subset L of the K antennas on each one of the Nbeamformers, based on quality indicators.
 13. The system according toclaim 12, wherein the quality indicator is respective contribution tototal data rate.
 14. The system according to claim 11, wherein thechannel fading rate is represented by measuring a mobility monitoringindicator (MMI).
 15. The system according to claim 11, wherein the TDTIis derivable via a lookup table based on a channel quality indicator(CQI) criterion and measured signal to noise plus interference ratio(SINR).
 16. The system according to claim 11, wherein the grading ofeach one of the K antennas is carried out by a process comprising:isolating a given antenna and registering the reported signal to noiseplus interference ratio (SINR) of each layer; converting each SINR toCQI and then to Data Rate via said lookup table; and summing the DataRates to provide total data throughput indicator (TDTI) grading, whilesaid process is carried out with K or less antennas at the otherbeamformers.
 17. The system according to claim 16, wherein the antennassubset selection and tuning module is further configured to update theSINR conversion in the lookup table in a case a new CQI report arrives.18. The system according to claim 11, wherein said tuning processincludes at least one round of coarse tuning process.
 19. The systemaccording to claim 11, wherein said coarse tuning process comprises:selecting best graded antenna as an anchor; combining the anchor withthe second best graded antenna and measure Total Data ThroughputIndicator (TDTI); flipping the phase of the second best antenna byapproximately 180°, and measuring the TDTI; choosing the better TDTI aspreferred coarse phase; combining the next best graded antenna with thepreviously combined antennas and measure the TDTI; flipping the phase ofthe next best graded antenna and measure TDTI, and selecting the betterTDTI as preferred coarse phase for the next best graded antenna;repeating the adding of antennas to the combiner per their grading untilall L antennas are added.